If your district has an account, this website allows you to search for 'editable' media. This means that you can use images (or even a frame from a video) and edit the image to suit your needs. Simply click on 'Advanced Search' under the 'Search' box, select 'Images' from the drop-down menu next to 'Media Type', and make certain that you have a check in front of 'Include only Editable Titles'.